Quick motorcycle question

S

sn95_311

Forum Member
So I'm working on an older bike for a guy and he tells me it's not charging. So after looking into the bike I noticed there wasn't a ground from the negative on the battery to the frame ( there was but it was like 16 gauge and really flimsy) so I added a 10g ground. Now when you start the bike and have the multimeter on the battery it will start to drop voltage at idle down to the point the bike will die. But if you hold it from 2-4k rpm the volts will increase up to like 13.5v and stay pretty steady and the bike will run forever and not die. But once at idle volts start to drop again.

Seem like the battery is just toast and not holding a decent charge ? New stator and regulator/rectifier.
 
What make and model is the bike? The output is on the low side- I typically want to see 14 vdc+ just above idle speed. The ground to the frame doesn't change much, given that the negative terminal runs to the engine, which is grounded to the frame anyway.
 
Yeah my 74 barley charges and my 73 was the same way. I ended up buying a newer style AGM battery, problem solved. The new battery is going on three years old now!
 
Something isn't right- you should be seeing at least 14vdc just off idle. Replace the battery for sure if it's more than a couple years old. I get lots of bad ones thru here from Meijer and Walmart type stores. Also, check to make sure one of the brake switches Isn't stuck, causing the brake light to stay on.
 
Also, check your stator to make sure none of the windings are shorted to ground. There should be continuity between all three wires, and none to ground with the stator unplugged. While the stator is unplugged, check the ac output from the stator. When the bike us revved up to 5-6k, you should see close to 100vac. Idle speed typically produces around 20vac. I have seen more than a few bad aftermarket stators and rectifier regulators.
 
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